Untitled

State Survey Summary Metrics for Species Distribution Shifts

Loading State Survey Data

We have secured state survey data from different survey programs along the East Coast of the US. These include the Maine and New Hampshire trawl survey, the Massachusetts trawl survey, Rhode Island trawl survey, Connecticut trawl survey, and the NEAMAP survey which spans a number of states up the east coast.

In the “NEAMAP_specimendata.rds” file, each row represents a single fish measured on NEAMAP, along with it’s length and an expansion factor. The expansion reflects the number of fish in the total catch of that species represented by that specimen. In other words, for a given species in a given tow, if you sum the expansion values, you wind up with the total catch in count for that species from that tow.

Centers of Abundance

Centers of abundance or biomass (mean or median) can be estimated from annual (or seasonal) catch data. These metrics give an indication of where the “heart” of a the catch is from a given survey. Movement in this metric (North, South, E/W etc.) could be evidence that the species is shifting its distribution.

Adjusted Centers

I added an option to the leading, trailing, edges function to correct for movement in the sampling effort. It takes whatever chunk of time we are estimating the leading, trailing, center metrics at, and it estimates how far the effort for that chunk of time deflects from the global (of whatever survey) center.